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Yesterday afternoon I noticed a bad taste in the back of my mouth. I chalked it up to post-nasal drip from seasonal allergies and tried to get on with my life. But by this afternoon, the bad taste had crept all the way forward and really set up shop. It colored everything I ate and drank, whether I was having a banana or a cup of coffee, whether I had just brushed my teeth or chewed a stick of gum or gargled with salt water, the bad taste didn't budge.

After I put aside yet another meal only half-eaten, I decided to do a bit of Googling. Among all the web pages suggesting that I might have a brain tumor (really) I noticed a mention of pine nuts. And then I remembered two things: having read about Pine Nut Mouth a few months ago, and having eaten pine nuts (for the first time in years) on Sunday.

How tragic, that such a nice Easter brunch with a friend of the family should result in… this.

Pine Nut Mouth is quite a mystery, albeit a well-documented one. It is a form of very mild poisoning which results in several days - possibly up to several weeks - of a syndrome called metallogeusia, which is the medical term for a lingering bitter, metallic taste. It causes no real harm, which is good, because there is no cure but time.

Pine nut toxicity is tentatively linked to pine nuts imported from China. The nuts have been tested and are free of any chemicals or heavy metal poisoning that researchers know could be toxic. The current theory is that it is caused by spoilage or oxidation of the pine nuts. It may also be something to do with a new species of pine nut being mixed in with the rest.

The reason why it's impossible to chase away the bad taste by eating or drinking something else is that the bad taste is actually happening in your brain, not in your mouth. Whatever substance causes the problem does so by interfering with the nerve impulses from your mouth to your brain. It's a misfire, in other words. But instead of producing a flash of light or sound, like a misfire in a car's engine would, this misfire produces a very bad taste.

Adding to the mystery of Pine Nut Syndrome is that it doesn't affect all people equally, and the CDC has been unable to find any chemical compound that would cause the problem. One batch that produced a lot of complaints came from Costco. In response, Costco sent samples of that batch plus a control that had received no complaints to several highly respected toxicology labs. None of the labs were able to find a difference between them. And the majority of people who had purchased and eaten the "bad" pine nuts showed no symptoms.

The FDA is continuing to examine the mystery of Pine Mouth. According to their website, most of the reports involve a particular species of Chinese pine nuts, and most of the nuts were consumed raw. If you experience a bout of Pine Mouth, you can report it to your state's FDA inspector here.